Inkjet printers eject drops of ink through an array of nozzles to effect printing on a media substrate. The nozzles are typically formed on a silicon wafer substrate using semiconductor fabrication techniques. Each nozzle is a MEMS (micro electro-mechanical systems) device driven by associated drive circuitry formed on the same silicon wafer substrate. The MEMS nozzle devices and associated drive circuitry formed on a single nozzle is commonly referred to as a printhead integrated circuit (IC).
Some inkjet printheads have a single printhead IC. These are scanning type printheads that traverse back and forth across the width of a page as the printer indexes the length of the page past the printhead. The Applicant has developed a range of pagewidth printheads that have a nozzle array as long as the printing width of the page. These printheads remain stationary in the printer as the page is fed past. This allows much higher print speeds but is more complicated in terms of controlling the operation of a much larger array of nozzles.
The pagewidth array of nozzles is made up of a series of separate printhead IC's placed end to end. Skilled workers in this field will appreciate that more printhead IC's can be fabricated on the unprocessed circular silicon wafers if each IC is short rather than long. Furthermore, localized fabrication defects can render an entire printhead IC defective. Hence there is less chance that each individual IC will be defective if they are shorter.
Unfortunately, the array of nozzles in one printhead IC can not simply abut the array of nozzles on an adjacent printhead IC. The sides of the printhead IC's can not be manufactured accurately enough to position the end nozzles of one IC close enough to the nozzles of the next IC without visible artifacts in the printed image. To ensure a seamless transition between the printing from adjacent IC's, the end portion of the nozzle array in one IC needs to overlap a portion of the nozzle array in the adjacent IC in a direction transverse to the paper feed direction. To do this, the overlapping portions need to be offset from each other along the paper feed path. In other words, the end nozzles in one array print to the media earlier in the paper path than the overlapping end nozzles of the adjacent nozzle array. This can be done by simply fabricating a triangular shaped end section of each nozzle array such that it is displaced further along the paper feed path than the remainder of the array (see FIG. 6A).
While this eliminates artifacts in the printing from the junction between adjacent IC's, it introduces a sharply angled section into the ink supply conduits for each nozzle row of each IC (see FIG. 6B). The sharp cornered supply conduits are prone to collect ‘outgassing’ bubbles (discussed in more detail below) and create additional resistance to the flow of supply ink to the displaced triangular section (which, for convenience the Applicant has termed ‘the drop triangle’).